1. Field of the Invention
The inventions disclosed and taught herein relate generally to methods and apparatuses for sulfiding, passivating and/or coking a hydrocarbon processing catalyst; and more specifically to methods and apparatuses for sulfiding, passivating and/or coking a hydrocarbon processing catalyst resident in a reactor.
2. Description of the Related Art
Hydroprocessing units, such as, but not limited to, hydrotreaters, hydrodesulfurizers and hydrocrackers, found in hydrocarbon refineries utilize metal sulfide catalysts to aid the chemical reactions. For example, and in general, hydrotreating processes use catalysts built on a γ-alumina substrate, and hydrocracking processes use catalysts with an alumina silicate substrate, which exhibit an acid function to aid in cracking the heavy hydrocarbons. These catalysts require periodic sulfiding to reach maximum catalytic activity. For purposes of this disclosure, “sulfiding” means converting a metal oxide on a catalyst to its metal sulfide.
There are several ways to sulfide catalyst already packed in a reactor vessel, commonly referred to as in-situ sulfiding, such as by using the naturally occurring sulfur in the hydrocarbon feed stock (aka sour feed). While beneficially avoiding the cost of an independent source of sulfur, using feedstock sulfur can be time consuming and potentially harmful if the sulfur content is not carefully monitored or high enough. An alternative to using feedstock sulfur is to use an independent sulfur source, such as, but not limited to, mercaptans, sulphides, disulphides, polysulphides and sulfoxides, such as Dimethyl Disulfide (DMDS), Dimethyl Sulfide (DMS), Dimethyl Sulfoxide (DMSO), di-tertiary-butyl polysulfide (TBPS), tertiary nonylpolysulfide (TNPS) and refinery acid gas. These sulfur sources can be used to perform in-situ liquid phase sulfiding or in-situ gas phase sulfiding.
In general, within the hydroprocessing unit, sulfur is reacted with hydrogen to form hydrogen sulfide (H2S). The metal oxide catalysts are reacted with hydrogen sulfide (H2S) and hydrogen (H2) at elevated temperatures to form the active metal sulfide, such as MoS2, Co9S8, WS2 or Ni3S2, in an exothermic reaction. Theoretically, only the stoichiometric amount of sulfur is needed to activate (i.e., sulfide) the catalyst. However, in the real world of commercial refineries, it is common to use more than the stoichiometric amount of sulfur to ensure complete activation. However, using excess sulfur creates excess hydrogen sulfide and other sulfiding products that must be disposed of or otherwise dealt with.
Liquid DMDS is often used as the sulfur source because of its high sulfur density by weight (compared to the other potential sulfur sources) and lack of solid or overly reactive decomposition products, which absence reduces coking. DMDS can be injected into the hydrocarbon feed stream as a liquid or into the hydrogen recycle loop as a gas. Under temperature and pressure, DMDS will decompose into H2S at several temperature ranges including about 350° F. to about 450° F.; about 390° F. to about 500° F. and about 450° F. to about 520° F.
Once the catalyst has been activated by converting the metal oxide to the metal sulfide form of the catalyst, the reactor usually must undergo a typically lengthy (e.g., several days) start-up procedure before the reactor can be returned to commercial or steady state operation. This start-up procedure is typically necessary because freshly sulfided catalysts may be overly reactive and using a reactive feed (e.g., cracked feed) at start up may cause fouling of the catalyst surface by formation of heavy cokes and gums. These fouling deposits may adversely limit the available active surface area and otherwise reduce the catalyst activity. Delaying the supply of cracked feeds to the unit during start-up by running first on a less reactive feed (primarily obtained through fractionation rather than cracking), usually referred to as “straight run” feed, allows these areas of high catalyst activity to moderate, thus minimizing adverse coke and gum formation when cracked feeds are introduced.
Typically, during start-up, straight run feed (in contrast to cracked feed) is supplied to the reactor. During this period, an amount of soft coke may form on the catalyst surface, which tempers or moderates the activity of the catalyst. Once catalyst activity has been passivated, cracked feeds can be fed to the reactor with reduced risk of adverse coke and gum formation.
The inventions disclosed and taught herein are directed to methods and apparatuses for efficiently sulfiding, sulfiding and passivating, sulfiding and coking, and/or sulfiding, passivating and coking catalysts packed in a reactor vessel.